Image sensor with reduced optical path

ABSTRACT

Among other things, one or more image sensors and techniques for forming image sensors are provided. An image sensor comprises a photodiode array configured to detect light. The image sensor comprises an oxide grid comprising a first oxide grid portion and a second oxide grid portion. A metal grid is formed between the first oxide grid portion and the second oxide grid portion. The oxide grid and the metal grid define a filler grid. The filler grid comprises a filler grid portion, such as a color filter, that allows light to propagate through the filler gird portion to an underlying photodiode. The oxide grid and the metal grid confine or channel the light within the filler gird portion. The oxide grid and the metal grid are formed such that the filler grid provides a relatively shorter propagation path for the light, which improves light detection performance of the image sensor.

BACKGROUND

An image sensor is a type of semiconductor device that converts anoptical input into an electrical signal. The image sensor comprises anarray of light detecting elements, such as photodiodes, where a lightdetecting element is configured to produce an electrical signalcorresponding to an intensity of light impinging on the light detectingelement. The electrical signal is used, in some instances, to display animage corresponding to the optical input.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a method of forming an imagesensor, according to some embodiments.

FIG. 2 is an illustration of a photodiode array of an image sensor,according to some embodiments.

FIG. 3 is an illustration of a first oxide layer of an image sensor,according to some embodiments.

FIG. 4 is an illustration of a metal layer of an image sensor, accordingto some embodiments.

FIG. 5 is an illustration of a second oxide layer of an image sensor,according to some embodiments.

FIG. 6 is an illustration of defining an oxide grid and a metal grid ofan image sensor, according to some embodiments.

FIG. 7 is an illustration of a capping layer of an image sensor,according to some embodiments.

FIG. 8 is an illustration of an image sensor detecting light, accordingto some embodiments.

FIG. 9 is a flow diagram illustrating a method of forming an imagesensor, according to some embodiments.

FIG. 10 is an illustration of a photodiode array of an image sensor,according to some embodiments.

FIG. 11 is an illustration of a first oxide layer of an image sensor,according to some embodiments.

FIG. 12 is an illustration of a metal layer of an image sensor,according to some embodiments.

FIG. 13 is an illustration of defining a metal grid of an image sensor,according to some embodiments.

FIG. 14 is an illustration of a capping layer and a second oxide layerof an image sensor, according to some embodiments.

FIG. 15 is an illustration of defining an oxide grid of an image sensor,according to some embodiments.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are generally used to refer tolike elements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providean understanding of the claimed subject matter. It is evident, however,that the claimed subject matter can be practiced without these specificdetails. In other instances, structures and devices are illustrated inblock diagram form in order to facilitate describing the claimed subjectmatter.

One or more image sensors and techniques for forming such image sensorsare provided herein. According to some embodiments, an image sensorcomprises a photodiode array formed over or within a substrate. Thephotodiode array comprises one or more photodiodes, such as image sensorpixels, configured to accumulate energy generated by light, such as fromphotons, of an optical input. A voltage of a photodiode is read as anoutput for the optical image. In some embodiments, a photodiode issituated under one or more layers or components formed over thesubstrate. Because light travels along a light propagation path thatcomprises such layers or components before reaching the photodiode,signal strength of the light can decay before reaching the photodiode orthe light can travel towards another photodiode that is not to detectthe light. Accordingly, as provided herein, an oxide grid portion and ametal grid portion, defining a filler grid that channels light towardsphotodiodes, are formed such that a light propagation path is reduced.Reducing the light propagation path improves performance of the imagesensor, such as improving a signal to noise ratio for the image sensoror improving color detection by the image sensor. The light propagationpath is reduced because the filler grid is defined as beingsubstantially between a top surface of a first oxide grid portion of theoxide grid and a top surface of a second oxide grid portion of the oxidegrid.

A method 100 of forming an image sensor, according to some embodiments,is illustrated in FIG. 1, and one or more image sensors formed by such amethodology are illustrated in FIGS. 2-8. An image sensor 200 comprisesa photodiode array 210 formed within a substrate 202, as illustrated inFIG. 2. In some embodiments, the photodiode array 210 comprises a firstphotodiode 204, a second photodiode 206, a third photodiode 208, orother photodiodes configured to detected light. At 102, a first oxidelayer 302 is formed over the photodiode array 210 as a first oxide girdportion 302 a of an oxide grid, as illustrated in FIG. 3. In someembodiments, the first oxide layer 302 has a height between about 500 Ato about 3000 A. In some embodiments, the first oxide layer 302 isformed by a deposition process.

At 104, a metal layer 402 is formed over the first oxide layer 302, asillustrated in FIG. 4. In some embodiments, the metal layer 402 has aheight between about 1000 A and about 3000 A. In some embodiments, themetal layer 402 has a width between about 0.1 microns and about 0.2microns. In some embodiments, the metal layer 402 is formed by a filmdeposition process.

At 106, a second oxide layer 502 is formed over the metal layer 402, asillustrated in FIG. 5. In some embodiments, the second oxide layer 502has a height between about 200 A to about 5000 A. In some embodiments,the second oxide layer 502 is formed by a deposition process. In someembodiments, a chemical mechanical polishing (CMP) process is performedafter deposition of the second oxide layer 502.

At 108, an etch 600 is performed through the second oxide layer 502 andthrough the metal layer 402 to form a metal grid 402 a and to form asecond oxide gird portion 502 a of the oxide grid, as illustrated inFIG. 6. The second oxide gird portion 502 a is formed over the metalgrid 402 a. The second oxide grid portion 502 a and the metal grid 402 adefine a filler grid 602 within which a fill material, such as a colorfilter material that guides light towards the photodiode array 210,could be formed. The filler grid is formed substantially between a topsurface 604 of the first oxide grid portion 302 a and a top surface 606of the second oxide grid portion 502 a. In some embodiments, a bottomsurface of the filler grid 602 is formed below the second oxide gridportion 502 a. In some embodiments, the bottom surface of the fillergrid 602 is formed below a top surface 608 of the metal grid 402 a.

In some embodiments, the filler grid 602 comprises a first filler gridportion 610 formed between a first metal grid structure 612 of the metalgrid 402 a and a second metal gird structure 614 of the metal grid 402a. In some embodiments, the first filler grid portion 610 is formedbetween a first oxide grid structure 616 of the second oxide gridportion 502 a and a second oxide grid structure 618 of the second oxidegrid portion 502 a. In some embodiments, the first filler grid portion610 is confined on a first side by the first oxide grid structure 616and the first metal grid structure 612. The first filler gird portion610 is confined on a second side by the second oxide grid structure 618and the second metal grid structure 614. The first filler grid structure610 is confined on a bottom side by the first oxide gird portion 302 a.

In some embodiments, a capping layer 702 is formed to line the fillergrid 602, as illustrated in FIG. 7. In some embodiments, the cappinglayer 702 comprises a material, such as an oxide film, used to protectthe metal grid 402 a, such as from moisture issues resulting from a fillmaterial used to fill the filler grid 602. In some embodiments, thecapping layer 702 is formed using a conformal oxide deposition process.In some embodiments, the capping layer 702 has a thickness between about200 A to about 1500 A. In some embodiments, the capping layer 702 isformed between the filler grid 602 and the first oxide gird portion 302a. In some embodiments, the capping layer 702 is formed between thefiller grid 602 and the metal grid 402 a. In some embodiments, thecapping layer 702 is formed between the filler grid 602 and the secondoxide grid portion 502 a.

FIG. 8 illustrates the second photodiode 206 of the image sensor 200detecting light 808. The image sensor 200 comprises one or more lensstructures, such as a first lens structure 802, a second lens structure804, and a second lens structure 806. In some embodiments, light 808,incident to the second lens structure 804, is focused towards the firstfiller grid structure 610 comprises a color filter material. The colorfilter material of the first filler grid structure 610 allows at leastsome of the light 808 to propagate towards the second photodiode 206. Atleast one of the first oxide grid portion 302 a of the oxide grid, thesecond oxide grid portion 502 a of the oxide grid, or the metal grid 402a confines the light 808 so that the light is detected by the photodiode206 as opposed to being detected by a different photodiode that is notto detect the light 808. Because the first filler grid structure 610 isconfined by the oxide grid and the metal grid 402 a, such as beingformed between the top surface 606 of the second oxide grid portion 502a and the top surface 604 of the first oxide grid portion 302 a asillustrated in FIG. 6, a light propagation path for the light 808 isreduced. Reducing the light propagation path improves performance of theimage sensor 200, such as improved detection of the light 808 by thesecond photodiode 206.

A method 900 of forming an image sensor, according to some embodiments,is illustrated in FIG. 9, and one or more image sensors formed by such amethodology are illustrated in FIGS. 10-15. An image sensor 1000comprises the photodiode array 210, comprising the first photodiode 204,the second photodiode 206, and the third photodiode 208, formed withinthe substrate 202, as illustrated in FIG. 10. At 902, the first oxidelayer 302 is formed over the photodiode array 210 as the first oxidegird portion 302 a of the oxide grid, as illustrated in FIG. 11. At 904,the metal layer 402 is formed over the first oxide layer 302, asillustrated in FIG. 12. At 906, a first etch 1300 is performed throughthe metal layer 402 to form the metal grid 402 a. In some embodiments ofperforming the first etch 1300, a hard mask is formed over the metallayer 402, such that a portion of the hard mark overlays a portion ofthe metal layer 402 to define the metal grid 402 a during the first etch1300.

In some embodiments, a capping layer 1400 is formed over the metal grid402 a, as illustrated in FIG. 14. In some embodiments, the capping layer1400 has a thickness between about 100 A to about 2000 A. In someembodiments, the capping layer 1400 comprises a nitride material or anoxide material. At 908, a second oxide layer 502 is formed over themetal grid 402 a, as illustrated in FIG. 14. In some embodiments, thesecond oxide layer 502 is formed over the capping layer 1400. In someembodiments, a CMP process is performed on the second oxide layer 502.At 910, a second etch 1500 is performed through the second oxide layer502 to form the second oxide grid portion 502 a of the oxide grid, asillustrated in FIG. 15. At least one of the oxide grid, such as thefirst oxide grid portion 302 a and the second oxide grid portion 502 a,or the metal grid 402 a define the filler grid 602. In this way, thefiller grid 602 is formed according to a multiple etch process.

According to an aspect of the instant disclosure, an image sensor isprovided. The image sensor comprises a photodiode array formed over asubstrate. The image sensor comprises a first oxide grid portion of anoxide grid. The first oxide grid portion is formed over the photodiodearray. The image sensor comprises a metal grid that is formed over thefirst oxide grid portion. The image sensor comprises a second oxide gridportion that is formed over the metal grid. The image sensor comprises afiller grid that is formed substantially between a top surface of thefirst oxide grid portion and a top surface of the second oxide gridportion.

According to an aspect of the instant disclosure, a method for formingan image sensor is provided. The method comprises forming a first oxidelayer over a photodiode array comprised within a substrate. The firstoxide layer is formed as a first oxide grid portion of an oxide grid. Ametal layer is formed over the first oxide layer. An etch is performedthrough the second oxide layer and the metal layer to form a metal gridand to form a second oxide grid portion of the oxide grid. The oxidegrid and the metal grid define a filler grid formed substantiallybetween a top surface of the first oxide grid portion and a top surfaceof the second oxide grid portion.

According to an aspect of the instant disclosure, a method for formingan image sensor is provided. The method comprises forming a first oxidelayer over a photodiode array comprised within a substrate. The firstoxide layer is formed as a first oxide grid portion of an oxide grid. Ametal layer is formed over the first oxide layer. A first etch isperformed through the metal layer to form a metal grid. A second oxidelayer is formed over the metal grid. A second etch is performed throughthe second oxide layer to form a second oxide gird portion of the oxidegrid. The oxide grid and the metal grid define a filler grid formedsubstantially between a top surface of the first oxide grid portion anda top surface of the second oxide grid portion.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter of the appended claims is not necessarily limited tothe specific features or acts described above. Rather, the specificfeatures and acts described above are disclosed as embodiment forms ofimplementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

It will be appreciated that layers, features, elements, etc. depictedherein are illustrated with particular dimensions relative to oneanother, such as structural dimensions or orientations, for example, forpurposes of simplicity and ease of understanding and that actualdimensions of the same differ substantially from that illustratedherein, in some embodiments. Additionally, a variety of techniques existfor forming the layers features, elements, etc. mentioned herein, suchas etching techniques, implanting techniques, doping techniques, spin-ontechniques, sputtering techniques such as magnetron or ion beamsputtering, growth techniques, such as thermal growth or depositiontechniques such as chemical vapor deposition (CVD), physical vapordeposition (PVD), plasma enhanced chemical vapor deposition (PECVD), oratomic layer deposition (ALD), for example.

Further, unless specified otherwise, “first,” “second,” or the like arenot intended to imply a temporal aspect, a spatial aspect, an ordering,etc. Rather, such terms are merely used as identifiers, names, etc. forfeatures, elements, items, etc. For example, a first channel and asecond channel generally correspond to channel A and channel B or twodifferent or two identical channels or the same channel.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally to be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B or the like generally means A or Bor both A and B. Furthermore, to the extent that “includes”, “having”,“has”, “with”, or variants thereof are used, such terms are intended tobe inclusive in a manner similar to “comprising”.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. An image sensor, comprising: a photodiode arrayoverlapping a substrate; a first oxide layer overlapping the photodiodearray; a metal grid comprising a first metal grid structure and a secondmetal grid structure in contact with a top surface of the first oxidelayer; an oxide grid comprising a first oxide grid structure in contactwith a top surface of the first metal grid structure and a second oxidegrid structure in contact with a top surface of the second metal gridstructure; a filler grid comprising a first filler grid structureoverlapping the first oxide layer and between the first metal gridstructure and the second metal grid structure; and a capping layer incontact with the top surface of the first oxide layer, wherein there isno metal between a top surface of the first oxide grid structure and alens structure overlapping the first oxide grid structure.
 2. The imagesensor of claim 1, wherein the capping layer is in contact with a bottomsurface of the first filler grid structure.
 3. The image sensor of claim1, wherein the first filler grid structure is between the first oxidegrid structure and the second oxide grid structure.
 4. The image sensorof claim 1, wherein the capping layer is in contact with the firstfiller grid structure.
 5. The image sensor of claim 1, wherein thecapping layer is in contact with the first metal grid structure andsecond metal grid structure.
 6. The image sensor of claim 1, wherein thecapping layer lines a sidewall of the first filler grid structure. 7.The image sensor of claim 1, wherein the lens structure in contact witha top surface of the capping layer.
 8. The image sensor of claim 1,wherein the first oxide layer overlaps a first photodiode of thephotodiode array, a second photodiode of the photodiode array, and aportion of the substrate between the first photodiode and the secondphotodiode.
 9. The image sensor of claim 1, wherein the first fillergrid structure comprises a color filter material configured to filterwavelengths within a defined range of wavelengths.
 10. An image sensor,comprising: a photodiode array comprising a first photodiode and asecond photodiode overlapping a substrate; a first oxide layeroverlapping the first photodiode, the second photodiode, and a portionof the substrate between the first photodiode and the second photodiode;a filler grid comprising a first filler grid structure and a secondfiller grid structure overlapping the first oxide layer; a metal gridcomprising a first metal grid structure between the first filler gridstructure and the second filler grid structure, wherein the first metalgrid structure is in contact with a top surface of the first oxidelayer; an oxide grid comprising a first oxide grid structure between thefirst filler grid structure and the second filler grid structure,wherein the first oxide grid structure is in contact with a top surfaceof the first metal grid structure; a capping layer in contact with thetop surface of the first oxide layer; and a lens structure overlappingthe first oxide grid structure, wherein there is no metal between a topsurface of the first oxide grid structure and the lens structure. 11.The image sensor of claim 10, wherein the lens structure is in contactwith a top surface of the capping layer.
 12. The image sensor of claim10, wherein the first filler grid structure comprises a color filtermaterial configured to filter wavelengths within a defined range ofwavelengths.
 13. The image sensor of claim 10, wherein the capping layeris in contact with the first oxide grid structure.
 14. The image sensorof claim 10, wherein the capping layer is in contact with the firstmetal grid structure and the first filler grid structure.
 15. The imagesensor of claim 10, wherein the capping layer is between the first oxidegrid structure and the first filler grid structure.
 16. The image sensorof claim 10, wherein the capping layer is in contact with the firstoxide grid structure and the first filler grid structure.
 17. The imagesensor of claim 10, wherein the capping layer is between the first oxidelayer and the first filler grid structure.
 18. The image sensor of claim10, wherein the capping layer is in contact with a bottom surface of thefirst filler grid structure.
 19. An image sensor, comprising: aphotodiode array in contact with a substrate; a first oxide layer incontact with the photodiode array and overlapping the substrate; a metalgrid comprising a first metal grid structure in contact with a topsurface of the first oxide layer; an oxide grid comprising a first oxidegrid structure in contact with a top surface of the first metal gridstructure; a capping layer in contact with the top surface of the firstoxide layer, the first metal grid structure, and the first oxide gridstructure, wherein there is no metal between a top surface of the firstoxide grid structure and a lens structure overlapping the first oxidegrid structure; and a filler grid comprising a first filler gridstructure in contact with the capping layer.
 20. The image sensor ofclaim 19, wherein the lens structure is in contact with a top surface ofthe capping layer.